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Generic Name: gentamicin
Brand Name: Garamycin (discontinued brand)
Drug Class: Aminoglycosides
What is gentamicin, and what is it used for?
Gentamicin is a broad-spectrum antibiotic used to prevent and treat many types of bacterial infections. Gentamicin is typically administered as intravenous or intramuscular injections for serious systemic infections. Gentamicin is also used as topical and ophthalmic formulations.
Gentamicin is effective against most gram-negative bacteria and staphylococcus species of gram-positive bacteria. Gram-negative and gram-positive bacteria are structurally different, and the types are identified by whether the bacteria get dyed or not in the Gram stain lab test.
Gentamicin enters into the bacterial cell, binds to the bacterial ribosomes (cellular particles that synthesize proteins) and interferes with the protein synthesis necessary for bacterial growth. This results in damage to the bacterial protein and cell membrane, resulting in its death.
Gentamicin is FDA-approved for use in the treatment of susceptible bacterial infections in adult and pediatric patients.
Off-label gentamicin uses in adults include the following:
- Prophylaxis for surgical infections (adults and children)
- Infective endocarditis (infection/inflammation of endocardium, heart’s inner lining)
- Infections in cystic fibrosis (a genetic disorder that affects fluid-secreting cells)
- Pelvic inflammatory disease
- Plague (Yersinia pestis)
Organisms susceptible to cefpodoxime include:
- Gram-positive bacteria:
- Staphylococcus species
Gram-negative bacteria:
- Citrobacter species
- Enterobacter species
- Escherichia coli
- Klebsiella species
- Proteus species
- Serratia species
- Pseudomonas aeruginosa
Warnings
- Do not use in patients with previous aminoglycoside toxicity or hypersensitivity
- Monitor patients closely for toxicity (nephrotoxicity and neurotoxicity)
- Gentamicin can cause damage to the kidney. The risk of nephrotoxicity is higher in patients undergoing high dosage prolonged therapy and in patients with impaired renal function
- Gentamicin is neurotoxic and can cause hearing loss and balance problems (ototoxicity). The risk of ototoxicity is higher in patients undergoing high dosage prolonged therapy and in patients with impaired renal function
- Use with caution in premature infants and newborn babies because the kidneys are not fully developed, which can prolong the serum half-life of the drug
- Neuromuscular blockade and respiratory paralysis have been reported following the use of aminoglycosides, especially when given soon after anesthesia or muscle relaxants; if blockage occurs, calcium salts may reverse these effects, but mechanical respiratory assistance may be necessary
- Avoid concurrent use with other neurotoxic or nephrotoxic drugs such as amikacin, streptomycin, neomycin, kanamycin, paromomycin
- Cumulative listing of drugs to avoid from all aminoglycosides include amphotericin B, bacitracin, cephaloridine, cisplatin, colistin, polymyxin B, vancomycin, and viomycin
- Avoid use of potent diuretics such as ethacrynic acid, furosemide because they increase the risk of ototoxicity; when administered intravenously, diuretics may enhance aminoglycoside toxicity by altering antibiotic concentrations in serum and tissue
What are the side effects of gentamicin?
Common side effects of gentamicin may include:
- Nephrotoxicity:
- Reduced urine output
- Kidney damage with reduced creatinine clearance
- Kidney damage when lowest drug concentration (trough) level exceeds 2 mg/L
- Neurotoxicity:
- Vertigo
- Dizziness
- Hearing loss
- Ringing in the ears (tinnitus)
- Balance problems (vestibular)
- Impaired coordination, balance and speech (ataxia)
- Gait instability
- Skin reactions including
- Injection site reactions including:
- Pain
- Irritation
- Redness (erythema)
- Less common side effects of gentamicin may include:
- Nausea
- Vomiting
- Loss of appetite (anorexia)
- Weight loss
- Increased salivation
- Inflammation of the intestines (enterocolitis)
- Allergic reaction
- Light sensitivity (photosensitivity)
- Redness of skin (erythema)
- Burning
- Stinging
- Headache
- Drowsiness (somnolence)
- Increase in intracranial pressure (pseudotumor cerebri)
- Elevated liver enzymes
- Low levels of white blood cells (granulocytopenia/agranulocytosis)
- Low platelet levels (thrombocytopenia)
- Shortness of breath (dyspnea)
- Tremors
- Muscle cramps
- Weakness
This is not a complete list of all side effects or adverse reactions that may occur from the use of this drug. Call your doctor for medical advice about serious side effects or adverse reactions. You may also report side effects or health problems to the FDA at 1-800-FDA-1088.
QUESTION
Bowel regularity means a bowel movement every day.
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What are the dosages of gentamicin?
Injectable solution
- 10 mg/ml
- 40 mg/ml
Adult
Susceptible Infections
Conventional dosing
- 3-5 mg/kg/day intravenously/intramuscularly (IV/IM) divided every 8 hours
Extended dosing interval (every 24 hours or more)
- Initial: 4-7 mg/kg/dose IV once/day
- Base dose on lean body weight
- Subsequent doses: Consult pharmacist
Surgical Infection Prophylaxis (Off-label)
- 5 mg/kg IV as single dose 1 hour prior to surgical incision; alternatively, 1.5 mg/kg IV as single dose for gynecology procedures
Infective Endocarditis Treatment (Off-label)
Enterococcus (native or prosthetic valve); Off-label dose
- 3 mg/kg/day IV/IM divided every 8 hour for 4-6 weeks in combination with a beta-lactam and for 6 weeks when administered with vancomycin
- Organism sensitivity testing should determine choice of concomitant antibiotic and treatment duration
S. aureus (prosthetic valve; methicillin susceptible or resistant); Off-label dose
- 3 mg/kg/day IV/IM divided every 8-12 hour for 3-5 days for native valve infections or for 2 weeks for prosthetic valve infections in combination with other antibiotics
- Organism sensitivity testing should determine choice of concomitant antibiotic
Viridans group streptococcus and S. bovis (native or prosthetic valve); Off-label use
- 3 mg/kg/day IV/IM every day (preferred) or divided every 8 hour for 2 weeks for native or prosthetic valve infections or for 6 weeks for prosthetic valve infections with relatively or fully resistant strains in combination with other antibiotic
- Organism sensitivity testing and source of infection should determine choice of concomitant antibiotic
Cystic Fibrosis (Off-label)
- 7.5-10.5 mg/kg/day intravenously/intramuscularly (IV/IM) divided every 8 hours
Pelvic Inflammatory Disease (Off-label)
- Loading dose: 2 mg/kg intravenously or intramuscularly (IV or IM)
- Maintenance dose: 1.5 mg/kg IV or IM every 8 hours
- May initiate transition from parenteral to oral therapy of either oral doxycycline or oral clindamycin within 24-48 hours of clinical improvement for total treatment duration of 14 days
Plague (Yersinia pestis) Treatment (Off-label)
- 5 mg/kg IV/IM every day for 10 days or 2 mg/kg IV/IM loading dose; then 1.7 mg/kg/dose IV/IM every 8 hour for 10-14 days or until 2 days after patient has no fever (afebrile); doxycycline, ciprofloxacin, or chloramphenicol could be used as third-line alternatives
Dosing Considerations
- Gentamicin may be given intravenously/intramuscularly (IV/IM)
- Dosing regimens are numerous and are adjusted based on CrCl and changes in the volume of distribution, as well as on the body space where the distribution of the agent will occur
- Monitor peak (4-12 mg/L) and trough (1-2 mg/L)
- Monitor renal and auditory function
- Each regimen must be followed by at least trough level drawn on a third or fourth dose, 30 minutes before dosing
- May draw peak level 30 minutes after a 30-minute infusion
- Use ideal body weight for mg/kg/dose; more accurate than total body weight
- Gentamicin is usually the first-line aminoglycoside against infections with gram-negative organisms such as Pseudomonas aeruginosa, Proteus, Escherichia coli, Klebsiella, Enterobacter, Serratia, and Citrobacter, as well as against Staphylococcus (gram-positive)
Dosing Modifications
Renal impairment
Conventional dosing
- Renally adjusted dose recommendations are based on doses of 1.7 mg/kg/dose every 8 hour or 5-7 mg/kg/dose once daily.
- CrCl more than 50 mL/min: No dosage adjustment necessary
- CrCl 10-50 mL/min: Administer every 12-48 hour
- CrCl less than 10 mL/min: Administer every 48-72 hour
Once daily (interval adjustment of extended interval dosing)
- Adjust doses based on serum concentrations and organism MIC
- CrCl of 60mL/min and above: No dosage adjustment necessary
- CrCl 40-59 mL/min: 5-7 mg/kg IV every 36 hour
- CrCl 20-39 mL/min: 5-7 mg/kg IV every 48 hour
- CrCl less than 20 mL/min: 5-7 mg/kg IV once; monitor serum levels and redose when gentamicin level is <1 mcg/mL
Intermittent hemodialysis
- Administer after hemodialysis on dialysis days
- Dependent on patient’s size, site of injection, filter, duration and type of intermittent hemodialysis, it is 30-50% dialyzable
- 1-1.7 mg/kg IV/IM after initial hemodialysis session; serum gentamicin concentrations should guide subsequent dosing
- Dosing dependent on assumption of 3 times/week complete intermittent hemodialysis sessions
Peritoneal dialysis
- Intermittent dosing: 0.6 mg/kg per exchange once daily for anuric patients; 0.75 mg/kg/dose IP for non-anuric patients per day during long dwell periods; depending on infecting organism and patient's clinical status, may treat for 2-3 weeks
- Continuous dosing: 8 mg/L loading dose; followed by 4 mg/L maintenance dose
- Continuous renal replacement therapy
- Drug clearance is highly dependent on method of renal replacement, filter type, and flow rate; close monitoring of pharmacologic response, sign of adverse reactions due to accumulation, and target drug concentration necessary for appropriate dosing
- 3 mg/kg/day IV/IM divided every 8 hours; may administer up to 5 mg/kg/day IV/IM divided every 6-8 hour in life-threatening infections; peak; adjust dose based on serum concentration monitoring; peak concentration higher than 12 mcg/mL should be avoided
Pediatric
Susceptible infections
Children below 5 years of age
- 2.5 mg/kg/dose IV/IM every 8 hours
Children 5 years of age and above and adolescents
- 2-2.5 mg/kg/dose intravenously/intramuscularly (IV/IM) every 8 hours
Infants under 30 weeks' gestation
- 0-28 days: 2.5 mg/kg/day IV/IM
- More than 28 days: 3 mg/kg/day IV/IM
Infants 30-36 weeks' gestation
- 0-14 days: 3 mg/kg/day IV/IM
- More than 14 days: 5 mg/kg/day IV/IM divided every 12 hours
Infants over 36 weeks' gestation
- 0-7 days: 5 mg/kg/day IV/IM divided every 12 hours
- More than 7 days: 7.5 mg/kg/day IV/IM divided every 8 hours
Surgical Prophylaxis, Preoperative (Off-label use)
- 2.5 mg/kg IV/IM within 60 minutes prior to surgical incision or without antibiotics; procedure dependent
- Dose is based on actual body weight unless it is more than 20% above ideal body weight; then dosage requirement may best be estimated using a dosing weight of IBW + 0.4 (TBW- IBW)
Dosage Modifications
- If GFR is greater than 50 mL/min/1.73m²: No dosage adjustment necessary
- GFR 30-50 mL/min/1.73m²: Administer every 12-18 hour
- GFR 10-29 mL/min/1.73m²: Administer every 18-24 hour
- If GFR is less than 10 mL/min/1.73m² Administer every 48-72 hour
Intermittent hemodialysis
- 2 mg/kg/dose; re-dose as indicated by serum concentration
Peritoneal dialysis
- 2 mg/kg/dose; re-dose as indicated by serum concentration
Continuous renal replacement therapy
- 2-2.5 mg/kg/dose every 12-24 hour; monitor serum concentration
Dosing Considerations
- Monitor peak (4-12 mg/L) and trough (1-2 mg/L)
- Monitor nephrotoxicity, neurotoxicity, and ototoxicity; assess at beginning of therapy and throughout
- Individualization critical due to low therapeutic index
- Use ideal body weight for mg/kg/dose, except in neonates (in whom actual body weight should be used)
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Overdose
- There is no antidote for gentamicin toxicity.
- In the event of overdose or toxic reactions, gentamicin may be removed from the blood with the aid of hemodialysis, especially if kidney function is compromised.
What drugs interact with gentamicin?
Inform your doctor of all medications you are currently taking, who can advise you on any possible drug interactions. Never begin taking, suddenly discontinue, or change the dosage of any medication without your doctor’s recommendation.
- Gentamicin has no known severe interactions with other drugs.
- Gentamicin has serious interactions with at least 26 different drugs.
- Gentamicin has moderate interactions with at least 163 different drugs.
- Gentamicin has mild interactions with at 76 different drugs.
The drug interactions listed above are not all of the possible interactions or adverse effects. For more information on drug interactions, visit the RxList Drug Interaction Checker.
It is important to always tell your doctor, pharmacist, or health care provider of all prescription and over-the-counter medications you use, as well as the dosage for each, and keep a list of the information. Check with your doctor or health care provider if you have any questions about the medication.
Pregnancy and breastfeeding
- Gentamicin can cause fetal harm. Avoid use in pregnant women except in life-threatening situations.
- Gentamicin enters breast milk. Use with caution in breastfeeding women.
What else should I know about gentamicin?
- Gentamicin is not intended for long-term therapy
- Use with caution in patients with:
- Renal failure (not on dialysis) or impairment
- Hearing impairment
- Neuromuscular disorders such as myasthenia gravis
- Conditions that depress neuromuscular transmission
- Electrolyte imbalances including low calcium (hypocalcemia), low magnesium (hypomagnesemia), or low potassium (hypokalemia)
- American Heart Association (AHA) Guidelines recommend endocarditis prophylaxis only for high-risk patients
